This Japanese site (selling energy drinks) (English auto-translate) mentions that during World War 2 eyeballs were plucked from fish, dried, and sent to the Japanese troops as a source of vitamin B1, and they also mention that there is a lot of DHA and EPA in them.

Unfortunately, though, I cannot find any information about them being pickled, but that would presumably be another way of delivering them to the front.

This Japanese site (selling energy drinks) (English auto-translate) mentions that during World War 2 eyeballs were plucked from fish, dried, and sent to the Japanese troops as a source of vitamin B1, and they also mention that there is a lot of DHA and EPA in them.

For your more simple question, here is a recipe for boiled in vinegar tuna eyeballs.